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SACRAMENTO – Two Seismic Hazard Zone
maps, each covering a 60-square-mile
area of Santa Clara County, became
official today. The maps, issued by the
California Department of Conservation,
impact local planners, developers,
property sellers and real estate agents.
If property is
located in a “zone of required
investigation,” where liquefaction or
landslides could occur during a large
earthquake, the local building
department must require geologic studies
before projects are issued permits.
Also, property sellers and real estate
agents must inform potential buyers if
property they're selling is in a Seismic
Hazard Zone, as is the case when
property is in a designated flood or
wildfire zone.
DOC’s California
Geological Survey released the Seismic
Hazard Zone maps for the Cupertino and
Los Gatos quadrangles in preliminary
form in March. They are now official
after public review and comment. The
maps are on file with local government
offices, including the planning
department, building department and
county recorder's office.
The northeastern half
of the Cupertino map includes parts of
the communities of Cupertino, Los Altos,
Los Altos Hills, Mountain View, San
Jose, Santa Clara, Saratoga and
Sunnyvale. The remainder of the
quadrangle is unincorporated, sparsely
populated county land.
Landslide hazard
zones occur extensively in the foothills
west of Cupertino westerly to the limits
of current zoning at the Santa Cruz
County line, extending from Foothill
College west of the Sierra Freeway,
southeasterly to Sanborn Skyline County
Park in Saratoga.
Liquefaction hazard
zones occur mostly along streams and
creeks in the metropolitan areas.
Notable are wide areas along Saratoga
Creek and Calabazas Creek in Saratoga,
Stevens Creek and Permanente Creek in
Cupertino and Sunnyvale.
Parts of the
communities of Los Gatos, San Jose,
Saratoga and Monte Sereno occupy the
northern quarter of the Los Gatos
quadrangle. The remainder of the
quadrangle is mostly steep, forested
terrain in the Santa Cruz Mountains that
is unincorporated county land.
Landslide hazard
zones occur over most of this map,
except the northern quarter, which is
the Los Gatos metropolitan area.
Liquefaction hazard
zones occur mostly along streams flowing
down from the slopes, notably Los Gatos
Creek from Lexington Reservoir north to
Vasona Reservoir in Los Gatos and Ross
Creek and Guadalupe Creek in San Jose.
Shaking causes most
of the damage during earthquakes, and in
many cases, it is cost effective to
retrofit houses and buildings to
minimize damage caused by severe
shaking. Local public libraries have a
number of publications by the Governor’s
Office of Emergency Services, American
Red Cross and the Federal Emergency
Management Agency that can be used as
guides to making homes more
earthquake-ready.
Seismic Hazard Zone
maps show areas at risk from the
secondary earthquake hazards of
landslides and liquefaction, which also
can be dangerous. It is generally not as
cost effective to retrofit an existing
building for the impacts of liquefaction
or landslides as it is to build in
safety features at the design stage.
Therefore, design changes to better
protect life and property during future
earthquakes are required before new
developments are approved and
constructed.
Eleven maps affecting
Northern California are now official.
The effort to identify and map seismic
hazards is ongoing. Preliminary Seismic
Hazard Zone maps for several East Bay
areas are scheduled for release in the
comings months.
Color copies of
official maps can be purchased through
DOC's California Geological Survey (415)
904-7707 or (916) 445-5716. The maps
also can be found on the Web
here.
In addition to
studying and mapping earthquakes and
other geologic phenomena, the Department
of Conservation maps and classifies
areas containing mineral deposits;
ensures reclamation of land used for
mining; regulates oil, gas and
geothermal wells; administers
agricultural and open-space land
conservation programs; and promotes
beverage container recycling.
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